Process for reforming hydrocarbons with an alumina-chromium oxide catalyst containing either germanium oxide, indium oxide, or gallium oxide



PROCESS FOR BEFORE ENG HYDROCARBONS WITH AN ALUMENA-CHROMIUM GE CATALYSTCGNTAENWG EITHER GERMA- NIUM GXIDE, ENDEUM ()XIDE, R GALLIUM OXIDEHarold A. Streclrer, Bedford, and Harrison M. Stine,

Lyndhurst, ()liio, asslgnors to The Standard Gil Company, Cleveland,Ohio, a corporation of Ghio No Drawing. Application Gctober 19, 1953,Serial No. 387,070

Claims priority, application Canada July 2, 1953 4 Claims. (Cl. 195-50)This invention relates to the catalytic conversion of hydrocarbons, andmore particularly to catalytic reforming.

In catalytic reforming, relatively light petroleum fractions, such asnaphthas and gasolines containing an appreciable amount of paramns andnaphthenes, are treated at an elevated temperature in the presence of acatalyst to alter their characteristics. The reforming reactions embracedehydrogenation, dehydrocyclization and aromatization of thehydrocarbons to produce fractions of approximately the same generalboiling range, but of different chemical structure and performancecharacteristics. A reformed product has a substantially increased octanenumber due in part to the increased aromatic content. Hydrogen isusually formed as one of the products.

v /hen the petroleum fraction is subjected to such a conversion,cracking usually takes place concurrently with the reforming. Thisapparently results from the fact that catalysts and reaction conditionsthat promote reforming also promote cracking more or less. It isbelieved that the cracked products polymerize under the reactionconditions, and that the end product of the polymerization is coke. Thiscoke formation is not primarily a product of the reforming. Rather it isbelieved that the coke results from the cracking-polymerizationreactions which take place concurrently with the reforming. As a result,a deposit of coke is laid down on the catalyst and the rate at whichthis coke is deposited depends upon the conditions of conversion andupon the catalyst. in general, conditions which give a high conversionlevel result in increased coke deposit. In most of the usual cases,especially those employing OXide type catalysts, the coke graduallydestroys the activity of the catalyst for promoting the desiredconversion. This loss in catalyst activity necessitates the 2,784,147Fatented Mar. 5, 1957 ever, coke formation is not eliminated by the useof hydrogen, and the process does not become non-regenerative even athydrogen partial pressures high enough for near complete repression ofthe reforming reactions.

Inasmuch as the use of hydrogen cannot completely prevent coke formationand only at best repress it, it is desirable to operate at lowerhydrogen partial pressures, and therefore lower total pressures, ifother variables can be selected which will give a low coke deposition atthe low pressures. Not only is the construction of reaction equipmentfacilitated by the use of low pressures, but the passage from thereforming to the regenerating cycle is facilitated if the reformingoperation is carried out at a low pressure. Regeneration'at highpressures is not particularly desirable and if the reaction pressure ishigh, complicated equipment, such as lock-s, must be provided forchanging the pressure between the reaction and the regeneration. If thepressure is sufficiently low, the difference between the reactionpressure and atmospheric regeneration pressure can be taken care of inthe fluid type equipment with'a leg of catalyst as is well understood inthe art. In addition, the relatively low hydrogen partial pressuresuseable with this catalyst provide an optimum yield-octane relation andminimiz butane production.

In accordance with our invention, we have discovered drogen partialpressure and low operating pressure, to

give a much higher level of conversion without any correspondingincrease in coke deposition, or from the alternative point of view, aminimization of coke deposition at the conversion levels, as comparedwith catalysts, previously known when operated under the same conversionconditions. The exact cause of the reduction of coke deposition by theaddition of such small amounts of these metal oxides is not fullyunderstood; however, it may be due to the fact that the concurrent andinherent manifestations attributable to cracking or polymerization orboth which accompany the reforming conversion are minimized withoutadversely affecting the reforming.

A surprising fact in connection with these catalysts is that theefiicacious reduction in coke deposition does not appear to be a commonfunction of closely related metal oxides functioning as third componentswhich might be expected to show similar properties,- but ratherapregeneration of the catalyst generally by burning oif the coke. It ishighly desirable, therefore, to provide processes using conditions and acatalyst which will" minimize the deposition of coke during. thereforming conversion.

This desirability of a minimum coke-producing reforming conversion iseconomically attractive from the stand point of savings in capitalexpenditure for regeneration .equipment, or the loss of on stream timeif the regenerato produce the same quality of product that is producedin the absence of hydrogen atlower temperatures. Howpears to be aspecific property of certain metal oxides. More particularly, it hasbeen found that wheii'oiiemetal oxide is ellicacious for this purpose,others of the same periodic group which might be expected to functionsimilarly'do' not do so. This is illustrative of the unpredictability ofthe oxides found to be suitable.

Prior U. S. Patent 2,236,514, assigned to our assignee, describes agel-type catalyst of alumina and chromium oxide in the proportions of 7(82 mol percent alumina and 18-30 mol percent chromium oxide formed bycoprecipitating precursors of these two ingredients. A preferredembodiment described in the patent consists in cop'r'ecipitatin acatalyst to provide mol percent alumina and 20 mol percent chromiumoxide by treating nitrates of the two metals with ammonia. Catalystswith proportions of the two oxides within the ranges'stat'ed may be madeby other co-precipitating methods such as the reaction of sodiumaluminate with a soluble chromium salt such as chromium nitrate orchromium acetate, with adjustment of the pH up to about 10, ifnecessary.

Merely as illustrative, such a catalyst may be prepared by mixingsolutions of chromium acetate and sodium aluminate in proportions toprovide a co-precipitated catalyst-having 76 mol percent of alumina and24 mol percent chromium oxide accompanied by the addition of sulfuricacid to maintain a pH of about 8.5. The catalyst is washed free ofsulfate, dried and has 3% volatiles at 1000 F.

This catalyst was used in a reforming operation employing a naphthahaving a Kattwinlrel number of about 10.5 (A. S. T. M. Standard MethodD87546T which is a measure of olefins and aromatics), an initial boilingpoint of 222 F., 50% over at 282 F. and an end point of 397 F. Thereforming conditions were as follows:

Temperature of conversion F. 980 Total pressure (gauge) 1 25 Hydrogen tonaphtha mol ratio 4.9 Hydrogen partial pressure (absolute) 1 33 Feedrate v./v./hr 1.32 On stream time minutes.... 30

1 Pounds per square inch.

The reformed product as obtained was analyzed for Kattwinkel number as ameasure of the reforming conversion. The catalyst after being flushedwith nitrogen and cooled was analyzed for coke by a conventional carbondetermination method utilizing combustion in a quartz tube. Thefollowing results are typical of the average of a large number ofconversions:

Kattwlnkel Number Coke, Wt.

Percent an 2. 2 57 3.1 58 3. 2 e2 3.

Kattwinkel numbers in the range of 55 to 65 correspond approximately tooctane numbers of 80-90 by the F-1 method.

Considering that coke percentages in excess of 3 to 3 4% are excessivefor a commercial operation, it will beseen that while this catalyst isone of the best avail- Kattwinkel Number Coke, Wt.

Percent It will be seen that the conversion level of this catalyst ismuch higher than those without the antimony oxide and represents one ofthe best catalysts up to this time that is available for operation underthese conditions.

In accordance with our invention we reform hydrocarbon fractions such asnaphthas and virgin gasolines, under reforming conditions utilizing alow pressure, and in the presence of a ctr-precipitated chromiumoxidealurnina catalyst impregnated with a relatively small amount of anoxide of a metal selected from the group consisting of germanium, indiumand gallium. While all, three components may be co-precipitated, we findthe catalyst entirely suitable when the chromia and alumina arectr-precipitated and the third element oxide incorpo rated byimpregnation. The catalyst base may be the same as that describedheretofore and may be made by the same methods, i. e., co-precipitationof alumina and chromium oxide within the ranges described heretofore.Catalysts used in the process of the invention may be impregnated with asolution of a salt or other compound of the third named element whichcan be converted to the oxide upon heating. The concentration of thesolution and the length of the impregnating time are such as toincorporate the desired amount of the third oxide which may be from 0.1to about 2.0 mol percent. Generally there is no advantage in using over1.0 mol percent and in the following examples good results were obtainedwith 0.2 to 0.4 mol percent of the third metal oxide. in general, thecatalyst is treated with the solution in a concentration of 0.05 to 0.5mol per liter. The catalyst may be treated with the impregnatingsolution for from a few minutes to several days, depending on theconcentration of the solution and the amount to be absorbed, the excesssolution drained away, and the catalyst dried. The catalyst is thenheated at a high temperature such as 850 to 1250 F. for a period of fourto twenty-four hours in an atmosphere of a gas such as dry nitrogen andcooled in the similar atmosphere. During this heating the impregnatingelement was converted to the oxide if it was not previously in thatform.

The catalyst may be in any of the usual physical forms, moreparticularly, in particles of any size or shape. If the catalyst isfinely divided, the reforming operation may be carried out with thecatalyst in a fluidized condition using the so-called fluid reformingtechnique. The catalyst may also be in larger particles, such as beads,which are more commonly used in the fixed and moving bed techniques.

The reforming operation is carried out under any of the usual reformingconditions provided the pressure is relatively low, which is anadvantage of our process. In general, the temperature will be between800 to 1200 F., preferably 900 to 1000 F. The total pressure will befrom atmospheric to about 50 pounds, preferably about 25 pounds. persquare inch gauge and the conversion conducted in the presence of addedhydrogen to provide a hydrogen partial pressure of about 10 to about 45pounds per square inch absolute. The rate of feed may be maintained atfrom about 0.3 to 10 volumes of hydrocarbon feed per volume of catalvstper hour.

The following examples are illustrative of catalysts which may be usedin accordance with our invention.

Example I A base reforming catalvst having a composition of 76 molpercent alumina and 2 m l nercent chromium oxide. co-nrecio tated asabove described. free of sulfate and having 3% vol tiles at 1fl00 F.. isim r nated with an ether s l ti n of germ nium tetrachloride in aconcentration of 0.05 mol er liter bv permitting the eatalvst to soak insuch a solution in the proportions of 2 nonnds of cata'lvst to 0.75pound of the ether solution of the germanium tetrachloride at roomtemperature for one hour. The excess solution was drained from thecatalyst which was then treated with 1 pound of water to convertgermanium tetrachloride to germanium oxide. Excess solution was a indrained and the remaining catalyst was dried at 300 F. for four hours.The catalyst was then heated for sixteen hours at 1000 F. in anatmosphere of drv nitrogen. cooled in nitrogen and bottled for testing.The catalvst contained 0.4 mol percent germanium oxide.

The same straight-run naphtha as described heretofore was passed throu hthe resulting catalyst under the same conditions described heretofore.The Kattwinkel number of the reformed naphtha was 58 and the coke on thecatalyst was 1.48%. This represents a reduction in the coke formation ascompared to the catalysts described heretofore, as can be seen by thefollowing comparison:

Two pounds of the catalyst base used in Example 1 were impregnated with1 pound of an aqueous solution containing 0.045 mol per liter of indiumnitrate. The drying procedure of Example 1 was then repeated. The amountof indium oxide in the catalyst was 0.2 mol percent. Using the samenaphtha and the same reforming conditions, the reformed product had aKattwinkel number of 57 and the catalyst had a coke content of 1.41%;The conversion level is satisfactory and the amount of coke well belowamounts obtained when the other catalysts are used, as is seen from thefollowing comparison:

Two pounds of the catalyst base used in Example 1 was treated with 1pound of aqueous solution containing 0.07 mol per liter gallium nitrate.The drying procedure was the same as in the previous examples. Theamount of the gallium oxide in the catalyst was about 0.4 mol percent.Using the same naphtha and the same reforming conditions, the reformedproduct had a Ka-ttwinkel number of 50 and the catalyst had a cokecon-tent of 1.1%. The catalyst compares favorably in results with thecatalyst described heretofore promoted by antimony, but the amount ofthe third component to achieve this result is substantially less. Thiscan be seen from the following table:

It is to be noted that the amount of third component oxide is quitesmall especially as compared with the amount of antimony described inthe prior art component catalyst and that the results are attractiveconsidering especially the relatively low hydrogen partial pressure andits advantages and the high conversion level and low coke formationindicated.

It can be readily seen from the preceding discussion that theincorporation of very small amounts of the oxides of the thirdcomponents on an alumina-chromia coprecipitated base catalyst gives asubstantial reduction in the rate of coke deposition at low hydrogenpartial pressures as compared with the alumina-chromium oxide basecatalyst or other three component catalysts heretofore available.

We claim:

1. The process for reforming petroleum fractions which comprisescontacting said fractions under reforming conditions including hydrogento provide a partial pressure of 1545 pounds per square inch absolute inthe presence of a co-precipitated alumina-chromium oxide catalystconsisting of alumina, chromium oxide, and a small proportion of a thirdcomponent oxide selected from a group consisting of germanium oxide,indium oxide and gallium oxide.

2. The process of claim 1 in which the co-precipitated alumina-chromiumoxide are in the proportions of -82 mol percent alumina to 3018 molpercent chromium oxide, and in which the oxide of the third component ispresent in the proportions of 0.1 to 2.0 mol percent.

3. The process of claim 1 in which the reforming operation is carriedout at a temperature of about 980 F. at a total pressure of about 25pounds per square inch gauge, at a hydrogen partial pressure of about 33pounds per square inch absolute, with a catalyst consisting of about75.8 mol percent alumina co-precipitated with about 23.8 mol percentchromium oxide, and about 0.2 to 0.4 mol percent of the oxide of thethird component.

4. The process of claim 2 in which the catalyst is finely divided andthe reforming is carried out With the catalyst in a fluidized form.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE PROCESS FOR REFORMING PETROLEUM FRACTIONS WHICH COMPRISESCONTACTING SAID FRACTION UNDER REFORMING CONDITIONS INCLUDING HYDROGENTO PROVIDE A PARTIAL PRESSURE OF 15-45 POUNDS PER SQUARE INCH ABSOLUTEIN THE PRESENCE OF A CO-PRECIPITATED ALUMINA-CHROMIUM OXIDE CATALYSTCONSISTING OF ALUMINA, CHROMIUM, OXIDE, AND A SMALL PROPORTION OF ATHIRD COMPONENT OXIDE SELECTED FROM A GROUP CONSISTING OF GERMANIUMOXIDE, INDIUM OXIDE AND GALLIUM OXIDE.